Thursday, May 14, 2015

Seafood and the story of evolution

Do you think that prawns are fish? If you are a fish eater, your Sunday meal may present you with the pleasant package of prawns and King Mackerel (Surmai in Marathi). Before you take the next mouthful, think about these two facts – prawns are not fish at all; and fish are actually closer to human beings that they are to prawns!
The story goes like this – prawns belong to a group of animals called the arthropods. Insects (like bees and ants) and spiders are some other kinds of animals that are also arthropods. Now arthropods is a very large group. In facts, 80% of all animals are arthropods. There are many smaller subgroups in the arthropods. We already know the insects. Then there are the arachnids, or what we call spiders. Do you know the centipedes – the round things with lots of legs? They have a group of their own, called myriapoda. And then there are crustaceans – the group of the prawns.
The crustaceans appeared on earth very early, around 50 crore years ago. There are other kinds of animals that fall in the crustacean subgroup, like crabs and lobsters. Crustaceans have mainly kept to the sea, not really showing much interest in venturing on the land.
Just like arthropods, there is another group called the chordates. It is much smaller, but a lot more important to us, because it’s the group to which we belong to.
The largest subgroup in chordates is vertebrates – animals with a backbone. All other subgroups are either very small or extinct.
After it gets here, the story becomes interesting, because it leads to us. In vertebrates, first come all the fish. Our topic of the day, the King Mackerel, is a member of a very important subgroup of the fishes – the bony fishes. About 99% of all fish belong to this group, almost every fish except the sharks. From the bony fish, it’s just three steps to us humans.
Once you leave out the fishes, most other vertebrates are tetrapods – animals with four limbs. There are only four major kinds of tetrapods – amphibians like the frogs, reptiles like the lizards and snakes, birds like the peacocks and mammals like humans. In fact, the tetrapods actually evolved from a kind of bony fish, an adventurous kind that crawled onto the land.
Can you see the picture now? Prawns the crustaceans broke away from chordates and vertebrates long time ago. But a branch of bony fish like Mackerel actually grew into early tetrapods and mammals- in turn, human beings.
So if prawns could talk, they would call us fish.